Also, check population and level before capturing the town and if it's near a city upgrade level, occupy it and hope that you can hold it long enough to build a governor's building --- this alone accounts for around 20% of culture penalty. The effect of replacing a temple is limited to 5% in my experience.

Anyway, to stick to the topic, has anyone figured out those adoption mechanics? I find it rather strange to be able to adopt certain temples which are identical to yours effect-wise and others not. I mean, is there any coherence in being to upgrade the ...say, temple of Horus (not sure about the name, though...one with equal law and happiness bonus) to the respective Armenian temple of Armazd while at the same time not being able to adopt temples of Zeus (Pontus, identical effect-wise)? The culture group doesn't seem to account since both Armenians and Pontics are Easterlings.